JP4986009B2 - Secondary battery - Google Patents

Description

The present invention relates to a secondary battery using a separator made of polyolefin or the like.

  With the remarkable development of portable electronic technology in recent years, electronic devices such as mobile phones and notebook computers have begun to be recognized as fundamental technologies that support an advanced information society. In addition, research and development related to the enhancement of the functions of these electronic devices have been energetically advanced, and the power consumption of these electronic devices has been increasing proportionally. On the other hand, these electronic devices are required to be driven for a long time, and a high energy density of a secondary battery as a driving power source has been inevitably desired.

  From the standpoint of the occupied volume and mass of the battery built in the electronic device, the higher the energy density of the battery, the better. At present, since lithium ion secondary batteries have an excellent energy density, they have been built into most devices.

  Usually, in lithium ion secondary batteries, lithium cobaltate is used for the positive electrode and a carbon material is used for the negative electrode, and the operating voltage is used in the range of 4.2V to 2.5V. In the unit cell, the terminal voltage can be increased to 4.2 V largely due to excellent electrochemical stability such as a non-aqueous electrolyte material or a separator.

By the way, in the conventional lithium ion secondary battery that operates at a maximum of 4.2 V, the positive electrode active material such as lithium cobaltate used for the positive electrode only uses about 60% of its theoretical capacity. Absent. For this reason, it is possible in principle to utilize the remaining capacity by further increasing the charging pressure. In fact, it is known that high energy density is manifested by setting the voltage during charging to 4.25 V or more (see Patent Document 1).
International Publication No. WO03 / 019713 Pamphlet

  However, in a battery in which the charging voltage is set to exceed 4.2 V, the oxidizing atmosphere is particularly strong in the vicinity of the surface of the positive electrode. As a result, the separator in physical contact with the positive electrode is oxidatively decomposed. There is a problem that battery characteristics such as cycle characteristics or high-temperature storage characteristics deteriorate.

The present invention has been made in view of such problems, and its purpose is to improve secondary battery characteristics such as cycle characteristics or high-temperature storage characteristics when the charging voltage is set to exceed 4.2V. To provide a battery.

In the secondary battery according to the present invention, the positive electrode and the negative electrode are arranged to face each other via a separator, and the open circuit voltage in a fully charged state per pair of the positive electrode and the negative electrode is in the range of 4.25V to 6.00V, A separator is coated on at least a part of a base material layer made of a polyolefin porous membrane and a positive electrode side surface of the base material layer, and is made of at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, and aramid. have a surface layer comprising, in a range thickness is 0.1μm or more 10μm or less of the surface layer, the thickness of the separator is within the scope of 5μm or 25μm or less.

According to the secondary battery of the present invention, since the open circuit voltage at the time of full charge is in the range of 4.25V to 6.00V, a high energy density can be obtained. Further, the separator has a surface layer made of at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene and aramid on at least a part of the surface on the positive electrode side of the base material layer made of a polyolefin porous film, Since the surface layer is coated on the surface of the base material layer, the thickness of the surface layer is in the range of 0.1 μm to 10 μm, and the thickness of the separator is in the range of 5 μm to 25 μm. Chemical stability can be improved and the occurrence of minute shorts can be suppressed. Therefore, the energy density can be increased, and battery characteristics such as cycle characteristics or high-temperature storage characteristics can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a cross-sectional structure of the secondary battery according to the first embodiment. This secondary battery is a so-called lithium ion secondary battery in which lithium (Li) is used as an electrode reactant and the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium. This secondary battery is called a so-called cylindrical type, and is a winding in which a pair of strip-like positive electrode 21 and strip-like negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. A rotating electrode body 20 is provided. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil. The positive electrode active material layer 21B includes, for example, one or more positive electrode materials capable of occluding and releasing lithium as a positive electrode active material, and a conductive agent such as graphite and polyfluoride as necessary. It is configured to contain a binder such as vinylidene.

As the positive electrode material capable of inserting and extracting lithium, for example, lithium-containing compounds such as lithium oxide, lithium phosphorus oxide, lithium sulfide, or an intercalation compound containing lithium are suitable. May be used in combination. In order to increase the energy density, a lithium-containing compound containing lithium, a transition metal element, and oxygen (O) is preferable. Among them, the transition metal element includes cobalt (Co), nickel, manganese (Mn), and iron. It is more preferable if it contains at least one of them. Examples of such lithium-containing compounds include lithium composite oxides having a layered rock salt structure shown in Chemical Formula 1, Chemical Formula 2 or Chemical Formula 3, lithium composite oxides having a spinel structure shown in Chemical Formula 4, or of 5 and lithium complex phosphate having a structure of olivine shown are listed, and _{specifically, LiNi 0.50 Co 0.20 Mn 0.30 O} 2, Li a CoO 2 (a ≒ 1), Li b NiO 2 (B≈1), Li _c1 Ni _c2 Co _1-c2 O ₂ (c1≈1, 0 <c2 <1), Li _d Mn ₂ O ₄ (d≈1), Li _e FePO ₄ (e≈1), etc. There is.

(Chemical formula 1)
Li _f Mn _(1-gh) Ni _g M1 _h O _(2-j) F _k
(In the formula, M1 is cobalt, magnesium (Mg), aluminum, boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron, copper (Cu), zinc (Zn), zirconium ( Zr), Molybdenum (Mo), Tin (Sn), Calcium (Ca), Strontium (Sr) and Tungsten (W) are represented by at least one of f, g, h, j and k, 0.8 ≦ f ≦ 1.2, 0 <g <0.5, 0 ≦ h ≦ 0.5, g + h <1, −0.1 ≦ j ≦ 0.2, 0 ≦ k ≦ 0.1 (Note that the composition of lithium varies depending on the state of charge and discharge, and the value of f represents a value in a fully discharged state.)

(Chemical formula 2)
Li _m Ni _(1-n) M2 _n O _(2-p) F _q
(In the formula, M2 represents at least one selected from the group consisting of cobalt, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, calcium, strontium, and tungsten. m, n, p and q are within the range of 0.8 ≦ m ≦ 1.2, 0.005 ≦ n ≦ 0.5, −0.1 ≦ p ≦ 0.2, 0 ≦ q ≦ 0.1. (Note that the composition of lithium varies depending on the state of charge and discharge, and the value of m represents a value in a fully discharged state.)

(Chemical formula 3)
Li _r Co _(1-s) M3 _s O _{(2-t) Fu}
(In the formula, M3 represents at least one selected from the group consisting of nickel, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, calcium, strontium, and tungsten. r, s, t, and u are values within the range of 0.8 ≦ r ≦ 1.2, 0 ≦ s <0.5, −0.1 ≦ t ≦ 0.2, and 0 ≦ u ≦ 0.1. Note that the composition of lithium varies depending on the state of charge and discharge, and the value of r represents the value in a fully discharged state.)

(Chemical formula 4)
Li _v Mn _2-w M4 _w O _x F _y
(In the formula, M4 represents at least one selected from the group consisting of cobalt, nickel, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, calcium, strontium, and tungsten. v, w, x and y are values in the range of 0.9 ≦ v ≦ 1.1, 0 ≦ w ≦ 0.6, 3.7 ≦ x ≦ 4.1, 0 ≦ y ≦ 0.1. (Note that the composition of lithium varies depending on the state of charge and discharge, and the value of v represents the value in a fully discharged state.)

(Chemical formula 5)
Li _z M5PO ₄
(Wherein M5 represents at least one selected from the group consisting of cobalt, manganese, iron, nickel, magnesium, aluminum, boron, titanium, vanadium, niobium, copper, zinc, molybdenum, calcium, strontium, tungsten and zirconium. Z is a value in the range of 0.9 ≦ z ≦ 1.1, wherein the composition of lithium varies depending on the state of charge and discharge, and the value of z represents the value in the fully discharged state.

In addition to these, examples of the positive electrode material capable of inserting and extracting lithium include inorganic compounds not containing lithium, such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS.

  The negative electrode 22 has, for example, a structure in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A having a pair of opposed surfaces. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. The anode current collector 22A is made of, for example, a metal foil such as a copper foil.

  The negative electrode active material layer 22B includes one or more negative electrode materials capable of inserting and extracting lithium as the negative electrode active material, and the positive electrode active material layer 21B as necessary. It is comprised including the binder similar to.

  In this secondary battery, the electrochemical equivalent of the negative electrode material capable of inserting and extracting lithium is larger than the electrochemical equivalent of the positive electrode 21, and lithium metal is deposited on the negative electrode 22 during charging. It is supposed not to.

  In addition, this secondary battery is designed so that the open circuit voltage (that is, the battery voltage) at the time of full charge is in the range of 4.25V to 6.00V. Therefore, even if the positive electrode active material is the same as that of the battery having an open circuit voltage of 4.20 V at the time of full charge, the amount of lithium released per unit mass is increased. Accordingly, the positive electrode active material and the negative electrode active material are increased accordingly. And the amount has been adjusted. As a result, a high energy density can be obtained.

  Examples of the negative electrode material capable of inserting and extracting lithium include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, and fired organic polymer compounds , Carbon materials such as carbon fiber or activated carbon. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and part of it is non-graphitizable carbon or graphitizable carbon. Some are classified as: Examples of the polymer material include polyacetylene and polypyrrole. These carbon materials are preferable because the change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Further, non-graphitizable carbon is preferable because excellent characteristics can be obtained. Furthermore, those having a low charge / discharge potential, specifically, those having a charge / discharge potential close to that of lithium metal are preferable because a high energy density of the battery can be easily realized.

  Examples of the negative electrode material capable of inserting and extracting lithium include materials capable of inserting and extracting lithium and containing at least one of a metal element and a metalloid element as a constituent element. . This is because a high energy density can be obtained by using such a material. In particular, the use with a carbon material is more preferable because a high energy density can be obtained and excellent cycle characteristics can be obtained. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of the metal element or metalloid element constituting the negative electrode material include magnesium, boron, aluminum, gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin, lead (Pb), Bismuth (Bi), cadmium (Cd), silver (Ag), zinc, hafnium (Hf), zirconium, yttrium (Y), palladium (Pd), or platinum (Pt) can be used. These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or a semimetal element in the short-period type periodic table as a constituent element is preferable, and at least one of silicon and tin is particularly preferable as a constituent element. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained.

  As an alloy of tin, for example, as a second constituent element other than tin, silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony (Sb), And those containing at least one member selected from the group consisting of chromium. As an alloy of silicon, for example, as a second constituent element other than silicon, among the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium The thing containing at least 1 sort (s) of these is mentioned.

  Examples of the tin compound or silicon compound include those containing oxygen (O) or carbon (C), and may contain the second constituent element described above in addition to tin or silicon.

Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds or polymer materials. Examples of other metal compounds include oxides such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ ), sulfides such as NiS and MoS, and lithium nitrides such as LiN _3. Examples include polyacetylene, polyaniline, and polypyrrole.

  The separator 23 includes a base material layer 23 </ b> A and a surface layer 23 </ b> B provided on the surface facing the positive electrode 21 or both surfaces. In FIG. 2, the surface layer 23 </ b> B is represented as being provided only on the surface facing the positive electrode 21.

  The base layer 23A is made of, for example, a porous film made of a synthetic resin such as polypropylene or polyethylene, and may have a structure in which two or more porous films are laminated. Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the base material layer 23A because it can obtain a shutdown effect within a range of 100 ° C. or higher and 160 ° C. or lower and is excellent in electrochemical stability. Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The surface layer 23B includes at least one selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, and aramid. Thereby, chemical stability improves and generation | occurrence | production of micro short-circuit is suppressed. In addition, when the surface layer 23B is formed of polypropylene, the base material layer 23A may be formed of polypropylene to be a single layer.

  The thickness of the surface layer 23B on the side facing the positive electrode 21 is preferably in the range of 0.1 μm to 10 μm. This is because if the thickness is small, the effect of suppressing the occurrence of micro-shorts is low, and if the thickness is large, the ion conductivity decreases and the volume capacity decreases.

The thickness of the separator 23 is preferably in the range of 5 μm to 25 μm. If the thickness is small, a short circuit may occur. If the thickness is large, the ionic conductivity is lowered and the volume capacity is lowered. Further, the air permeability of the separator 23 is a value converted to a thickness of 20 μm, and is preferably in the range of 200 seconds / 100 cm ³ or more and 600 seconds / 100 cm ³ or less. This is because when the air permeability is low, a short circuit may occur, and when the air permeability is high, the ion conductivity decreases. Furthermore, the porosity of the separator 23 is preferably in the range of 30% to 60%. This is because if the porosity is low, the ionic conductivity is lowered, and if it is high, a short circuit may occur. In addition, the puncture strength of the separator 23 is a value converted to a thickness of 20 μm, and is preferably in the range of 0.020 N / cm ² or more and 0.061 N / cm ² or less. This is because if the piercing strength is low, a short circuit may occur, and if the piercing strength is high, the ionic conductivity decreases.

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains a solvent and an electrolyte salt dissolved in the solvent.

  As the solvent, cyclic carbonates such as ethylene carbonate or propylene carbonate can be used, and it is preferable to use one of ethylene carbonate and propylene carbonate, particularly a mixture of both. This is because the cycle characteristics can be improved.

  As the solvent, in addition to these cyclic carbonates, it is preferable to use a mixture of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate or methylpropyl carbonate. This is because high ionic conductivity can be obtained.

  It is preferable that the solvent further contains 2,4-difluoroanisole or vinylene carbonate. This is because 2,4-difluoroanisole can improve discharge capacity, and vinylene carbonate can improve cycle characteristics. Therefore, it is preferable to use a mixture of these because the discharge capacity and cycle characteristics can be improved.

  In addition to these, examples of the solvent include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3- Dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethyl Examples include imidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, and trimethyl phosphate.

  A compound obtained by substituting at least a part of hydrogen in these non-aqueous solvents with fluorine may be preferable because the reversibility of the electrode reaction may be improved depending on the type of electrode to be combined.

As electrolyte salt, lithium salt is mentioned, for example, 1 type may be used independently, and 2 or more types may be mixed and used for it. Lithium salts include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, difluoro [oxolato-O, O ′] lithium borate, lithium bisoxalate borate, or LiBr. Among them, LiPF ₆ is preferable because it can obtain high ion conductivity and can improve cycle characteristics.

  For example, the secondary battery can be manufactured as follows.

  First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like material. A positive electrode mixture slurry is prepared. Next, the positive electrode mixture slurry is applied to the positive electrode current collector 21 </ b> A, the solvent is dried, and the positive electrode active material layer 21 </ b> B is formed by compression molding using a roll press or the like, thereby forming the positive electrode 21.

  Further, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry Is made. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, the solvent is dried, and the negative electrode active material layer 22B is formed by compression molding with a roll press machine or the like, and the negative electrode 22 is manufactured.

  Subsequently, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.

  In this secondary battery, when charged, lithium ions are released from the positive electrode active material layer 21B, and the negative electrode material that can occlude and release lithium contained in the negative electrode active material layer 22B via the electrolytic solution. Occluded. Next, when discharging is performed, lithium ions stored in the negative electrode material capable of inserting and extracting lithium in the negative electrode active material layer 22B are released, and are inserted into the positive electrode active material layer 21B through the electrolytic solution. . Here, since the separator 23 has the above-described configuration, the chemical stability is improved, and even if the open circuit voltage at the time of full charge is increased, the occurrence of minute shorts is suppressed and the battery characteristics are improved. The

  As described above, in this embodiment, since the open circuit voltage at the time of full charge is in the range of 4.25 V to 6.00 V, a high energy density can be obtained. In addition, since the separator is provided with a layer made of at least one member selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, and aramid on at least the side facing the positive electrode 21, the chemical stability of the separator 23 is improved. Performance can be improved, and the occurrence of minute shorts can be suppressed. Therefore, the energy density can be increased, and battery characteristics such as cycle characteristics or high-temperature storage characteristics can be improved.

(Second Embodiment)
The secondary battery according to the second embodiment of the present invention is a so-called lithium metal secondary battery in which the capacity of the negative electrode is represented by a capacity component due to precipitation and dissolution of lithium as an electrode reactant.

  This secondary battery has the same configuration and effects as those of the secondary battery according to the first embodiment except that the configuration of the negative electrode active material layer 22B is different. Therefore, with reference to FIG. 1 and FIG. 2, the same code | symbol is attached | subjected to a corresponding component and description of the same part is abbreviate | omitted.

  The negative electrode active material layer 22B is made of lithium metal that is a negative electrode active material, and can obtain a high energy density. The negative electrode active material layer 22B may be configured to be already provided from the time of assembly, but may be configured by lithium metal which is not present at the time of assembly and is deposited during charging. The negative electrode active material layer 22B may also be used as a current collector, and the negative electrode current collector 22A may be deleted.

  This secondary battery is different from the secondary battery except that the negative electrode 22 is made of only the negative electrode current collector 22A, lithium metal alone, or lithium metal is attached to the negative electrode current collector 22A to form the negative electrode active material layer 22B. Can be manufactured in the same manner as the secondary battery according to the first embodiment.

  In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 21 and deposited as lithium metal on the surface of the negative electrode current collector 22A via the electrolyte, as shown in FIG. Then, the negative electrode active material layer 22B is formed. When the discharge is performed, for example, lithium metal is eluted as lithium ions from the negative electrode active material layer 22B, and is occluded in the positive electrode 21 through the electrolyte. Here, since the separator 23 has the above-described configuration, the chemical stability is improved, and even if the open circuit voltage at the time of full charge is increased, the occurrence of minute shorts is suppressed and the battery characteristics are improved. The

(Third embodiment)
The secondary battery according to the third embodiment of the present invention includes a capacity component due to insertion and extraction of lithium, which is an electrode reactant, and a capacity component due to precipitation and dissolution of lithium, and the sum thereof. It is represented by.

  This secondary battery has the same configuration and effect as the first or second secondary battery except that the configuration of the negative electrode active material layer is different, and can be manufactured in the same manner. Therefore, here, description will be made with reference to FIGS. 1 and 2 using the same reference numerals. Detailed descriptions of the same parts are omitted.

  For example, the negative electrode active material layer 22B has an open circuit voltage (that is, a battery voltage) in the charging process by making the charge capacity of the negative electrode material capable of occluding and releasing lithium smaller than the charge capacity of the positive electrode 21. When lithium is lower than the overcharge voltage, lithium metal begins to deposit on the negative electrode 22. Therefore, in this secondary battery, both the negative electrode material capable of inserting and extracting lithium and lithium metal function as a negative electrode active material, and the negative electrode material capable of inserting and extracting lithium is lithium metal. It is a base material for precipitation.

  The overcharge voltage refers to the open circuit voltage when the battery is overcharged. For example, the safety of lithium secondary batteries is one of the guidelines established by the Japan Storage Battery Industry Association (Battery Industry Association). Refers to a voltage that is higher than the open circuit voltage of a “fully charged” battery as defined and defined in the “Evaluation Criteria Guidelines” (SBA G1101). In other words, it refers to a voltage higher than the open circuit voltage after charging using the charging method, standard charging method, or recommended charging method used when determining the nominal capacity of each battery.

  This secondary battery is the same as the conventional lithium ion secondary battery in that a negative electrode material capable of inserting and extracting lithium is used for the negative electrode 22, and lithium metal is deposited on the negative electrode 22. Is the same as a conventional lithium metal secondary battery, but by depositing lithium metal on a negative electrode material capable of inserting and extracting lithium, high energy density can be obtained and cycle characteristics can be obtained. In addition, the quick charge characteristics can be improved.

  In this secondary battery, when charged, lithium ions are released from the positive electrode 21 and are first inserted into the negative electrode material capable of inserting and extracting lithium contained in the negative electrode 22 through the electrolytic solution. When charging is further continued, lithium metal begins to deposit on the surface of the negative electrode material capable of inserting and extracting lithium in a state where the open circuit voltage is lower than the overcharge voltage. After that, lithium metal continues to deposit on the negative electrode 22 until charging is completed. Next, when discharging is performed, first, lithium metal deposited on the negative electrode 22 is eluted as ions, and is occluded in the positive electrode 21 through the electrolytic solution. When the discharge is further continued, lithium ions occluded in the negative electrode material capable of occluding and releasing lithium in the negative electrode 22 are released and inserted in the positive electrode 21 through the electrolytic solution. Here, since the separator 23 has the above-described configuration, the chemical stability is improved, and even if the open circuit voltage at the time of full charge is increased, the occurrence of minute shorts is suppressed, and the battery characteristics are improved. The

(Fourth embodiment)
FIG. 3 shows a configuration of a secondary battery according to the fourth embodiment of the present invention. In this secondary battery, a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached is accommodated in a film-like exterior member 40, and can be reduced in size, weight, and thickness. ing.

  The positive electrode lead 31 and the negative electrode lead 32 are led out from the inside of the exterior member 40 to the outside, for example, in the same direction. The positive electrode lead 31 and the negative electrode lead 32 are each made of a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, the exterior member 40 is disposed so that the polyethylene film side and the wound electrode body 30 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 4 shows a cross-sectional structure taken along line II of the spirally wound electrode body 30 shown in FIG. The wound electrode body 30 is obtained by stacking and winding a positive electrode 33 and a negative electrode 34 with a separator 35 and an electrolyte layer 36 interposed therebetween, and the outermost peripheral portion is protected by a protective tape 37.

  The positive electrode 33 has a structure in which a positive electrode active material layer 33B is provided on one or both surfaces of a positive electrode current collector 33A. The negative electrode 34 has a structure in which a negative electrode active material layer 34B is provided on one surface or both surfaces of a negative electrode current collector 34A, and the negative electrode active material layer 34B side is disposed so as to face the positive electrode active material layer 33B. Yes. The configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 are the same as those of the positive electrode current collector 21A and the positive electrode described in the first to third embodiments. This is the same as the active material layer 21B, the negative electrode current collector 22A, the negative electrode active material layer 22B, and the separator 23.

  The electrolyte layer 36 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 36 is preferable because high ion conductivity can be obtained and battery leakage can be prevented. The configuration of the electrolytic solution (that is, the solvent, the electrolyte salt, and the like) is the same as that of the secondary battery according to the first to third embodiments. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, from the viewpoint of electrochemical stability, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable.

  For example, the secondary battery can be manufactured as follows.

  First, a precursor solution containing a solvent, an electrolyte salt, a polymer compound, and a mixed solvent is applied to each of the positive electrode 33 and the negative electrode 34, and the mixed solvent is volatilized to form the electrolyte layer 36. After that, the positive electrode lead 31 is attached to the end of the positive electrode current collector 33A by welding, and the negative electrode lead 32 is attached to the end of the negative electrode current collector 34A by welding. Next, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are laminated via a separator 35 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and a protective tape 37 is adhered to the outermost peripheral portion. Thus, the wound electrode body 30 is formed. Finally, for example, the wound electrode body 30 is sandwiched between the exterior members 40, and the outer edges of the exterior members 40 are sealed and sealed by heat fusion or the like. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 33 and the negative electrode 34 are prepared as described above, and after the positive electrode lead 31 and the negative electrode lead 32 are attached to the positive electrode 33 and the negative electrode 34, the positive electrode 33 and the negative electrode 34 are stacked via the separator 35 and wound. Rotate and adhere the protective tape 37 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 30. Next, the wound body is sandwiched between the exterior members 40, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 40. Subsequently, an electrolyte composition including a solvent, an electrolyte salt, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and the exterior member Inject into 40.

  After injecting the electrolyte composition, the opening of the exterior member 40 is heat-sealed and sealed in a vacuum atmosphere. Next, heat is applied to polymerize the monomer to obtain a polymer compound, thereby forming a gel electrolyte layer 36, and assembling the secondary battery shown in FIG.

  The operation and effect of the secondary battery are the same as those of the secondary battery according to the first to third embodiments.

  Furthermore, specific examples of the present invention will be described in detail.

(Examples 1-1 to 1-4)
A battery in which the capacity of the negative electrode 22 is represented by a capacity component due to insertion and extraction of lithium, that is, a lithium ion secondary battery was manufactured. At that time, the battery was as shown in FIG.

First, a positive electrode active material was prepared. After mixing commercially available nickel nitrate, cobalt nitrate, and manganese nitrate as aqueous solutions so that the molar ratios of Ni, Co, and Mn are 0.50, 0.20, and 0.30, respectively, with sufficient stirring Ammonia water was added dropwise to the mixed solution to obtain a composite hydroxide. This composite hydroxide and lithium hydroxide were mixed, baked at 900 ° C. for 10 hours using an electric furnace, and then pulverized to obtain a lithium composite oxide powder as a positive electrode active material. When the obtained lithium composite oxide powder was analyzed by atomic absorption spectrometry (ASS), the composition of LiNi _0.50 Co _0.20 Mn _0.30 O ₂ was confirmed. Further, when the particle diameter was measured by a laser diffraction method, the average particle diameter was 13 μm. Furthermore, when X-ray diffraction measurement was performed, it was similar to the pattern of LiNiO ₂ described in 09-0063 of the ICDD (International Center for Diffraction Data) card, and a layered rock salt structure similar to LiNiO ₂ was formed. It was confirmed that Furthermore, when observed with a scanning electron microscope (SEM), spherical particles in which primary particles of 0.1 μm to 5 μm aggregated were observed.

The obtained LiNi _0.50 Co _0.20 Mn _0.30 O ₂ powder, graphite as a conductive agent, polyvinylidene fluoride as a binder, LiNi _0.50 Co _0.20 Mn _0.30 O ₂ powder: graphite: polyvinylidene fluoride = 86: 10: A positive electrode mixture was prepared by mixing at a mass ratio of 4. Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is uniformly applied to both surfaces of a positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm and dried. Then, the cathode active material layer 21B was formed by compression molding with a roll press machine, and the cathode 21 was produced. The thickness of the positive electrode 21 was set to 150 μm. After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

Further, a negative electrode mixture is prepared by mixing spherical graphite powder having an average particle diameter of 30 μm as a negative electrode active material and polyvinylidene fluoride as a binder at a mass ratio of spherical graphite powder: polyvinylidene fluoride = 90: 10. Prepared. Subsequently, the anode mixture was dispersed in N- methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry was uniformly coated on the both surfaces of the anode current collector 22A made of a strip-shaped copper foil having a thickness of 15 [mu] m, heating The negative electrode 22 was fabricated by press molding to form the negative electrode active material layer 22B. The thickness of the negative electrode 22 was set to 160 μm. After that, a nickel negative electrode lead 26 was attached to one end of the negative electrode current collector 22A. In addition, the electrochemical equivalent ratio of the positive electrode 21 and the negative electrode 22 was designed so that the capacity | capacitance of the negative electrode 22 was represented by the capacity | capacitance component by occlusion and discharge | release of lithium.

After each of the positive electrode 21 and the negative electrode 22 was prepared, a microporous membrane separator 23 was prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 were laminated in this order, and this laminate was wound many times in a spiral shape. A jelly roll type wound electrode body 20 was produced. As shown in Table 1, in Example 1-1, the separator 23 was coated with polyvinylidene fluoride so that the thickness was 2 μm on each side of the base material. In Example 1-2, the base material was base material. The surface opposite to the positive electrode 21 is coated with polytetrafluoroethylene so that the thickness is 7 μm. In Example 1-3, the both surfaces of the base material are coated with polypropylene so that the thickness is 2 μm. In Example 1-4, the surface on the side facing the positive electrode 21 of the base material was coated with aramid so as to have a thickness of 3 μm. Further, the substrate was polyethylene thickness 16 [mu] m.

  After producing the wound electrode body 20, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The wound electrode body 20 was housed inside a nickel-plated iron battery can 11. Thereafter, 4.0 g of electrolyte solution was injected into the battery can 11 by a reduced pressure method.

In the electrolytic solution, 1.5 mol of LiPF ₆ as an electrolyte salt was mixed with a solvent in which ethylene carbonate, dimethyl carbonate, and vinylene carbonate were mixed in a mass ratio of ethylene carbonate: dimethyl carbonate: vinylene carbonate = 35: 60: 1. What was dissolved so that it might become / kg was used.

  After injecting the electrolyte into the battery can 11, the battery lid 14 is caulked to the battery can 11 through the gasket 17 whose surface is coated with asphalt, whereby Examples 1-1 to 1-4 have a diameter of 14 mm. A cylindrical secondary battery having a height of 65 mm was obtained.

  As Comparative Example 1-1 with respect to Examples 1-1 to 1-4, a secondary battery was obtained in the same manner as in Examples 1-1 to 1-4 except that polyethylene having a thickness of 16 μm was used as the separator 23. Was made.

  The obtained secondary batteries of Examples 1-1 to 1-4 and Comparative Example 1-1 were examined for high-temperature storage characteristics and cycle characteristics.

High-temperature storage characteristics, in a constant-temperature bath set to 60 ° C., at a constant current of 1000 mA, after the battery voltage constant current charge was performed until reaching 4.4V, when subjected to constant-voltage charge at 4.4V The fluctuation of the charging current value, that is, the float characteristic was obtained. The results are shown in FIG.

The cycle characteristics are as follows. First, constant current charging was performed at a constant current of 1000 mA until the battery voltage reached 4.40 V, then constant voltage charging was performed at a constant voltage of 4.40 V for 1 hour, and then at a constant current of 2000 mA. A constant current discharge is performed until the battery voltage reaches 3V, and this charge / discharge is repeated, and the discharge capacity maintenance rate in any cycle with respect to the discharge capacity in the first cycle (discharge capacity in any cycle / discharge capacity in the first cycle) × was determined as 100 (%). The results of Example 1-3 and Comparative Example 1-1 are shown in FIG.

  As can be seen from FIG. 5, in Examples 1-1 to 1-4 using the separator 23 coated with polyvinylidene fluoride, polypropylene, polytetrafluoroethylene, or aramid, the rising of the charging current was observed over time. In Comparative Example 1-1 using a separator not coated with these, rising of the charging current was observed after about 70 hours, and it was confirmed that a minute short circuit occurred.

  Moreover, as can be seen from FIG. 6, according to Example 1-3 using the separator 23 coated with polypropylene, each time the cycle was repeated, as compared with Comparative Example 1-1 using a separator not coated with polypropylene. The decrease in the discharge capacity maintenance rate was small.

  That is, in a battery having an open circuit voltage in the range of 4.25 V or more and 6.00 V or less during full charge, at least a part of the positive electrode side of the separator 23 is made of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, and aramid. It was found that battery characteristics such as cycle characteristics or high-temperature storage characteristics can be improved by using at least one of the above.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above embodiments and examples, the case where lithium is used as the electrode reactant has been described. However, other Group 1A elements such as sodium (Na) or potassium (K), or magnesium or calcium (Ca), etc. The present invention can also be applied to the case of using the 2A group element, other light metals such as aluminum, lithium, or alloys thereof, and the same effects can be obtained. At that time, as the negative electrode active material, the negative electrode material described in the above embodiment can be used in the same manner.

  In the above embodiments and examples, the secondary battery having a winding structure has been described. However, the present invention is similarly applied to a secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. be able to. In addition, the present invention can also be applied to a so-called coin type, button type, or square type secondary battery.

It is sectional drawing showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG. It is a disassembled perspective view showing the structure of the secondary battery which concerns on other embodiment of this invention. It is sectional drawing along the II line | wire of the winding electrode body shown in FIG. It is a characteristic view showing the float characteristic in the secondary battery produced in the Example. It is a characteristic view showing the cycle characteristic in the secondary battery produced in the Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20, 30 ... Winding electrode body, 21, 33 ... Positive electrode, 21A, 33A ... Positive electrode current collector, 21B, 33B ... Positive electrode active material layer, 22, 34 ... Negative electrode, 22A, 34A ... Negative electrode current collector, 22B, 34B ... Negative electrode active material layer, 23, 35 ... Separator , 23A ... base material layer, 23B ... surface layer, 24 ... center pin, 25, 31 ... positive electrode lead, 26, 32 ... negative electrode lead, 36 ... electrolyte layer, 37 ... protective tape, 40 ... exterior member, 41 ... adhesive film .

Claims (5)

The positive electrode and the negative electrode are arranged to face each other with a separator interposed therebetween,
The open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is in the range of 4.25V to 6.00V,
The separator is coated on at least a part of a base material layer made of a polyolefin porous membrane and a positive electrode side surface of the base material layer, and at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, and aramid. possess and become more surface layer,
The thickness of the surface layer is in the range of 0.1 μm to 10 μm, and the thickness of the separator is in the range of 5 μm to 25 μm.
Secondary battery.   The secondary battery according to claim 1, wherein the base material layer includes at least one of polyethylene and polypropylene.   The secondary battery according to claim 1, wherein the negative electrode includes a carbon material, and the carbon material includes at least one of graphite, graphitizable carbon, and non-graphitizable carbon. Before Symbol range air permeability thickness 20μm value of 200 sec / 100 cm ³ or more 600 sec / 100 cm ³ or less in terms of the separator and a porosity in the range of 30% to 60%, a piercing strength thick It is within the range of 0.020 N / cm ² or more and 0.061 N / cm ² or less as a value converted to 20 μm.
The secondary battery according to claim 1.   The secondary battery according to claim 1, which is a lithium secondary battery.

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